Intramedullary nails are used to aid in the healing of fractured bones. A nail is implanted in the medullary canal of the bone across the fracture site in order to position the bone fragments and provide load-bearing support so that the patient can move about while the bone is healing. The nail is secured to the bone by a series of locking screws or fixation bolts, which must pass through holes in the nail and into the surrounding bone material.
After the nail is inserted into the medullary canal, the distal end of the nail is no longer visible to the eye. The nail can be viewed with the use of an X-ray or other radiation source because it is constructed of stainless steel or other radiopaque material. The nail will cast a dark, elongate image on the X-ray monitor, while the nail holes will appear as light circles or ovals. In particular, a nail hole will appear as a circle when the X-ray source is positioned such that the X-ray beam is parallel to the axis of the nail hole.
In order to secure the nail to the bone, a trocar or scalpel is used to make an incision through the soft tissue to the bone material, and a drill is used to drill through the nail hole and surrounding bone material for insertion of the locking screw. An aiming guide is used with the X-ray source in order to accurately position the trocar and surgical drill over the nail holes.
Various aiming guides are already known in the art, such as those disclosed in U.S. Pat. Nos. 4,969,889, 4,917,111, and 5,478,343. In general, each of those devices has a handle portion constructed of a radiolucent material, such as plastic, which is relatively invisible to X-rays and thus will not cast a strong image on the X-ray monitor. Certain radiopaque aiming components, such as metal rings or other structures, are attached to or located within the distal end of the radiolucent handle. The radiopaque components will cast a definite image on the X-ray monitor when the X-ray source is turned on. The aiming guide is then positioned over the nail in such a manner that the image(s) cast by the radiopaque aiming components is (are) superimposed over the circular image of the nail hole on the X-ray monitor. Once the aiming guide is properly positioned over the nail hole, a trocar is used to make an incision to the surface of the bone above the nail hole, and a drill can be used to drill accurately through the nail hole and surrounding bone material for insertion of the locking screws.
Certain aiming guides, such as that disclosed in U.S. Pat. No. 4,969,889, contain substantial radiopaque components and thus tend to be rather heavy and bulky. Other aiming guides, such as that disclosed in U.S. Pat. No. 5,478,343, require the simultaneous manipulation of more than one instrument in order to locate and drill through the nail hole. Also, the protection sleeves and trocars used in the prior art were constructed entirely or substantially of metal, which made them heavy and tended to obstruct the view on the X-ray monitor. A more compact, unitary, and lighter weight aiming guide having fewer radiopaque components would prove advantageous.